Early Exercise vs. Breast Cancer Risk

A new study shows that girls and young women who exercise regularly can substantially lower their risk of pre-menopausal breast cancer.

One-fourth of all breast cancers are diagnosed before menopause.

After monitoring 65,000 women, researchers found that those who were physically active had a 23 percent lower risk of breast cancer before menopause. High levels of physical activity between ages 12 to 22 were key to lowering breast cancer risk.

"We don't have a lot of prevention strategies for pre-menopausal breast cancer, but our findings clearly show that physical activity during adolescence and young adulthood can pay off in the long run by reducing a woman's risk of early breast cancer," says lead investigator Graham Colditz, M.D., Dr. P.H., of the Washington University School of Medicine.

Even better, it did not take heroic amounts of exercise to see a payoff. The levels of physical activity reported by the most active subjects were the equivalent of running 3.25 hours a week or walking 13 hours a week.

"You don't have to be a marathon runner to get the risk-reducing benefits of exercise," Colditz adds.

One leading theory to explain the lower risk of breast cancer among active young women is that exercise reduces their exposure to the hormone estrogen, which increases breast cancer risk. Women who begin menstruating later have a lower risk of breast cancer and young women who are physically active are more likely to start their periods later.

The study, by researchers at Washington University School of Medicine in St. Louis and Harvard University in Boston, appears online in the May 13 Journal of the National Cancer Institute.